Buggy code:
public class Check < T > extends LabeledWebMarkupContainer { private static final long serialVersionUID = 1L ; private static final String ATTR_DISABLED = "disabled" ; private int uuid = - 1 ; private final CheckGroup < T > group ; public Check ( String id ) { } public Check ( String id , IModel < T > model ) { } public Check ( String id , CheckGroup < T > group ) { } public Check ( String id , IModel < T > model , CheckGroup < T > group ) { } public String getValue ( ) { } @ SuppressWarnings ( "unchecked" ) protected CheckGroup < T > getGroup ( ) { } @ Override protected void onComponentTag ( final ComponentTag tag ) { super . onComponentTag ( tag ) ; checkComponentTag ( tag , "input" ) ; checkComponentTagAttribute ( tag , "type" , "checkbox" ) ; CheckGroup < ? > group = getGroup ( ) ; final String uuid = getValue ( ) ; tag . put ( "name" , group . getInputName ( ) ) ; tag . put ( "value" , uuid ) ; Collection < ? > collection = ( ( Collection < ? > ) ( group . getDefaultModelObject ( ) ) ) ; if ( collection == null ) { throw new org . apache . wicket . WicketRuntimeException ( ( ( "CheckGroup<seq2seq4repair_space>[" + ( group . getPath ( ) ) ) + "]<seq2seq4repair_space>contains<seq2seq4repair_space>a<seq2seq4repair_space>null<seq2seq4repair_space>model<seq2seq4repair_space>object,<seq2seq4repair_space>must<seq2seq4repair_space>be<seq2seq4repair_space>an<seq2seq4repair_space>object<seq2seq4repair_space>of<seq2seq4repair_space>type<seq2seq4repair_space>java.util.Collection" ) ) ; } if ( group . hasRawInput ( ) ) { final String [ ] inputArray = group . getInputAsArray ( ) ; if ( inputArray != null ) { for ( String input : inputArray ) { if ( uuid . equals ( input ) ) { tag . put ( "checked" , "checked" ) ; } } } } else if ( collection . contains ( Check . getDefaultModelObject ( ) ) ) { tag . put ( "checked" , "checked" ) ; } if ( group . wantOnSelectionChangedNotifications ( ) ) { CharSequence url = group . urlFor ( INTERFACE ) ; Form < ? > form = group . findParent ( Form . class ) ; if ( form != null ) { tag . put ( "onclick" , form . getJsForInterfaceUrl ( url ) ) ; } else { <START_BUG> tag . put ( "onclick" , ( ( ( ( "window.location.href='" + url ) + ( ( url . toString ( ) . indexOf ( '?' ) ) > ( - 1 ) ? "&amp;" : "?" ) ) + ( group . getInputName ( ) ) ) + "='<seq2seq4repair_space>+<seq2seq4repair_space>this.value;" ) ) ; <END_BUG> } } if ( ( ( ! ( isActionAuthorized ( ENABLE ) ) ) || ( ! ( Check . isEnabledInHierarchy ( ) ) ) ) || ( ! ( group . isEnabledInHierarchy ( ) ) ) ) { tag . put ( Check . ATTR_DISABLED , Check . ATTR_DISABLED ) ; } final String marker = "wicket-" + ( getGroup ( ) . getMarkupId ( ) ) ; String clazz = tag . getAttribute ( "class" ) ; if ( Strings . isEmpty ( clazz ) ) { clazz = marker ; } else { clazz = ( clazz + "<seq2seq4repair_space>" ) + marker ; } tag . put ( "class" , clazz ) ; } public Check < T > setLabel ( IModel < String > labelModel ) { } @ SuppressWarnings ( "unchecked" ) public final IModel < T > getModel ( ) { } public final void setModel ( IModel < T > model ) { } @ SuppressWarnings ( "unchecked" ) public final T getModelObject ( ) { } public final void setModelObject ( T object ) { } @ Override protected boolean getStatelessHint ( ) { } }

Fix:
tag . put ( "onclick" , ( ( ( ( "window.location.href='" + url ) + ( ( url . toString ( ) . indexOf ( '?' ) ) > ( - 1 ) ? "&" : "?" ) ) + ( group . getInputName ( ) ) ) + "='<seq2seq4repair_space>+<seq2seq4repair_space>this.value;" ) ) ;